This invention relates generally to an optical fiber module for converting an electrical signal into an optical signal and for converting an optical signal into an electrical signal, and more particularly to an optical fiber module for easily converting an electric cable into an optical cable.
There is already known an optical fiber module (disclosed in Japanese Patent Unexamined Publication No. 3-218134) as shown in FIG. 22. FIG. 22 is a plan view showing the conventional optical fiber module, and in the conventional optical fiber module, LD (laser diode) modules 1 for transmitting an optical signal, PD (photodiode) modules 2 for receiving an optical signal, semiconductor ICs 4 and 5 for converting an optical signal into an electrical signal, connectors 6 for feeding electrical signals to a mother board (not shown) and for receiving electrical signals from the mother board, and so on are mounted on a printed circuit board 3 having a width of 76 mm and a length of 75 mm.
FIG. 23 is a cross-sectional view of a main portion of the conventional optical fiber module, showing a lower frame 7b (disclosed in Japanese Patent Unexamined Publication No. 3-218134), and the conventional optical fiber module has been fixed to the mother board (not shown) by spacers 8 and J-clips 9 formed on the lower frame 7b.
However, the prior art technique has the following problems:
1) Recently, with the development and spread of computer systems, a transmission system capable of effecting a low-noise, long-distance transmission has become necessary. An optical signal transmission, using optical fibers, is excellent with respect to noises and a transmission distance as compared with an electrical signal transmission, and has drawn attention. However, from the viewpoint of the cost, a mother board for an optical fiber module has not been mounted on most of the current systems, and a module for electrical signals has been mounted on most of the systems. Therefore, when trying to change a heretofore-used electric cable to an optical cable capable of achieving a low-noise transmission and a long-distance transmission, it is necessary to incorporate a mother board, having an optical fiber module mounted thereon, into the system, and therefore the optical signal transmission, using the optical fibers, could not be easily achieved. PA1 2) In the conventional optical fiber module, when an optical connector portion of the optical module is to be inserted into an opening of the system, and an optical plug is to be inserted reversely, the optical connector portion is limited by the opening of the system, thereby preventing the reverse insertion of the optical plug. A fitting portion of the optical connector of the conventional optical fiber module is constituted by two (upper and lower) resin frames, and when the optical connector is forcibly inserted with its right and left sides reversed, the frames are opened in an upward-downward direction because of the elasticity of the resin, so that the reverse insertion, which should be impossible, occurs, which has invited problems with respect to the function and safety. PA1 3) The conventional optical fiber module has been fixed to a back panel of a host computer or the like through the motherboard, and therefore a frame of the optical fiber module need only to have a sufficient strength to withstand the force of insertion and withdrawal of the optical connector. However, an optical fiber module of the present invention is used alone, and therefore needs to withstand various external forces. PA1 4) The conventional optical fiber module has operated in an extension slot in integrally-connected relation to the mother board, and therefore it has not been necessary to provide a shield on the whole of the optical fiber module. However, the optical fiber module of the present invention operates alone at high speed outside an extension slot, and therefore it is necessary to suppress unnecessary radiation, and a shield needs to be provided over the whole of the optical fiber module. PA1 5) Considerable heat is generated from ICs mounted on the printed circuit board, and a sufficient space has been provided around each semiconductor IC, so that heat radiation due to heat diffusion can be expected. However, a printed circuit board of the optical fiber module of the present invention is confined in a narrow space defined by a cover, and therefore heat radiating means is necessary for enhancing the reliability. PA1 6) The electric connector of the conventional optical fiber module is fixed to the printed circuit board only by soldering, and there has not been provided any fixing means for fixing the electric connector to a box-like member of the optical fiber module, and stresses, developing when inserting and withdrawing the electric connector, concentrate on the soldered portions by which the electric connector and the printed circuit board are connected together, and the reliability has been insufficient with respect to damage to contacts of the electric connector and damage to a land. PA1 7) In the conventional optical fiber module, the process of adjusting a light-emitting power of the LD, which is harmful to the human body and particularly to the eyes, has been effected in the condition of the finished product, and therefore an opening for adjusting purposes needs to be provided in a cover or other part of the optical fiber module. However, external electromagnetic waves and the like have intruded through this opening to greatly lower the reliability of the optical fiber module. To prevent these electromagnetic waves, a metal seal or the like has been bonded, and this has increased the cost of the optical fiber module.
Therefore, the present invention seeks to easily achieve an optical signal transmission, using the existing electrical signal transmission system, and an object of the invention is to provide an optical fiber module which is compact, and can be produced at low costs, and has high reliability.